1. Field of the Invention
The present invention relates to a method and a device for pacing an image reader at a constant scanning speed, to stabilize the speed of a drive motor in an image reader, e.g. such as a copying machine, scanner or the like, thereby keeping a constant speed in reading an image.
2. Description of the Related Art
An image reader, such as a copying machine, scanner, etc., used to read and process image data on an original of a paper sheet etc. comprises a light source lamp such as a fluorescent lamp to irradiate light beams on an original and a light receptor with a photoelectric converter device such as CCD (Charge-Coupled Device) to receive the reflected light. The image reader for stationary original such as described in Japanese Laid-Open Patent Application No. 1998-257252 irradiates light beams onto an original on a platen glass, with a moving light source lamp. Then, a reflector or the like is arranged to guide the reflected light beams to the light receptor and is also adapted to travel along the original together with the light source lamp, as required to keep constant the optical path length from the original to the light receptor, without being affected by the change in position of the irradiating light beams on the original.
In recent years, such image data read out by this kind of image reader are not only outputted on a paper sheet but transferred into personal computers for various uses where higher image quality and more faithful reproducibility than ever before are required, based on more precisely obtained image data.
To obtain more precise image data, various ideas have been tried including structures to keep a drive motor working at a constant speed, preventing the vibration of the drive motor from being transmitted to the light source lamp, to thereby keep the light source lamp traveling at a constant speed.
On the other hand, the drive motor has a little irregularity in rotation by its own nature, causing speed fluctuations to result also in irregularity in traveling speed of the light source lamp, sometimes failing to obtain image data precisely enough to satisfy the requirements for high image quality. This type of speed fluctuations, caused by the characteristics of the drive motor itself, cannot always be eliminated by a known structure where an inertia spindle is conventionally used to smooth the rotation.